1. Field of the Invention
The present invention relates to a thrust bearing, and more particularly, to a thrust bearing that improves ease of handling by integrally assembling a bearing washer, rolling elements and cage in a non-separated form, thereby improving ease of assembly when assembling for use in, for example, automobile steering or other general mechanical apparatuses.
2. Description of the Prior Art
An example of this type of thrust bearing of the prior art is shown in FIGS. 1 and 2. Furthermore, said thrust bearing is disclosed in Japanese Laid-Open Patent Publication No. 57-114031. As shown in the drawings, this thrust bearing is equipped with a first bearing washer 1 and a second bearing washer 2, arranged so that each track la and track 2a faces the other, a plurality of rolling elements in the form of rollers 3, arranged and juxtaposed along the circumferential direction between said tracks la and 2a, and a cage 4 formed into a circular shape that holds and guides these rollers 3. Together with cylindrical flanges 1b and 2b being formed bent and extending in the axial direction on the outside of each first bearing washer 1 and second bearing washer 2, flat tracks 1a and 2a are formed on the inside in a single plane with said first bearing washer 1 and second bearing washer 2. In addition, second bearing washer 2 is inserted into first bearing washer 1.
Window-shaped, punched out holes 1c, in this case two, are formed at equally arranged locations along the circumferential direction in flange 1b of first bearing washer 1. Projections 1d, which protrude toward the inside, are formed at locations on the leading edge of said flange 1b that correspond to these punched out holes 1c.
On the other hand, projection 2d, which protrudes toward the outside, is formed in the leading edge of flange 2b formed on second bearing washer 2. As a result of projection 2d engaging with the above-mentioned projection 1d of first bearing washer 1, first bearing washer 1 and second bearing 2 are prevented from separating, thus resulting in all component members being integrally assembled in a non-separated form.
A second example of a thrust bearing of the prior art is shown in FIGS. 3 and 4. Furthermore, this thrust bearing is disclosed in Japanese Laid-Open Patent Publication No. 61-137116.
As shown in the drawings, said thrust bearing is equipped with a first bearing washer 11, on which cylindrical flanges 11a and 11b are provided bent and extending in mutually opposing directions in their respective axial directions on the outside and inside, a second bearing washer 12, formed into the shape of a flat plate and inserted into said first bearing washer 11 so that its track 12a relatively faces track 11c of said first bearing washer 11, rolling elements in the form of rollers 13, arranged and juxtaposed along the circumferential direction between said tracks 11c and 12a, and cage 14 formed into a circular shape that holds and guides these rollers 13.
Projections 11d, which protrude toward the inside, are formed at equally arranged locations along the circumferential direction on the leading edge of flange 11a of first bearing washer 11. In addition, notch 12b, which is chamfered and has a cross-section in the shape of a triangle, is formed in the corner at which the outer circumferential surface and outer surface intersect the second bearing washer 12, and the above-mentioned projections 11d, formed in first bearing washer 11, are inserted into this notch 12b. As a result, first bearing washer 11 and second bearing washer 12 are prevented from separating, thus resulting in all the component members being integrally assembled in a non-separated form.
In the thrust bearing shown in FIGS. 1 and 2 as a first example of the prior art, cylindrical flanges 1b and 2b are formed in both a first bearing washer 1 and a second bearing washer 2. The normal process for forming bearing washers having these flanges first involves obtaining flat, circular, semi-finished products by applying sheet steel, which is used for the raw material, to a press forming machine. Drawing is then performed on the outer edges of the semi-finished products by using a press forming machine to form the above-mentioned flanges 1b and 2b. Next, hardening is performed on the portions serving as the above-mentioned tracks 1a and 2a using, for example, cementation. Furthermore, carbon prevention treatment is performed on those portions where the above-mentioned projections 1d are formed at the time of the above-mentioned hardening, after which the projections 1d are formed in final process. In addition to this type of forming being complex and not always easy, it is also difficult to achieve a reduction in costs.
In addition, although projections 1d are formed as locking portions for the first bearing washer 1 to prevent first bearing washer 1 and second bearing washer 2 from separating, since these projections 1d are extremely small, there is the risk of the amount of protrusion of the projections will not reach the specified value (due to forming error and so forth) during forming of the projections 1d, or that the locking mechanism will not align in the case where the finished thrust bearing is handled poorly.
In addition, in this constitution, debris, moisture and other harmful foreign objects are able to easily penetrate inside the thrust bearing from outside. Conversely, grease and other lubricants filled inside the thrust bearing can easily leak to the outside, thus resulting in the disadvantage of replenishment of lubricant having to be performed relatively frequently in order to maintain favorable bearing function over a long period of time.
Moreover, in addition to the above factors, it has become desirable in recent years to develop thrust bearings that are able to secure a required load capacity while having compact size. Incidentally, in the above-mentioned constitution, since cylindrical flange 2b is formed on the second bearing washer 2, the outer diameter becomes larger at that portion.
On the other hand, for the thrust bearing shown in FIGS. 3 and 4 as a second example of the prior art, the second bearing washer 12 is formed into a simple flat plate. This can be easily obtained by performing press forming on the sheet steel used for raw material, and then performing hardening at the site which is to serve as track 12a.
However, cylindrical flanges 11a and 11b are provided on the outside and inside of the first bearing washer 11. The forming of a bearing washer having two flanges in this manner is even more difficult to obtain and results in higher costs than the forming of a bearing washer having one flange, such as that equipped on the thrust bearing as a first example of the prior art described above.
In addition, in this thrust bearing, projections 11d, in the form of locking portions formed on first bearing washer 11 to prevent the first bearing washer 11 and the second bearing washer 12 from being separated in the same manner as the thrust bearing indicated as a first example of the prior art, are extremely small. Thus, there is the risk of the locking by the projections 11d becoming misaligned. In addition, there are also similar problems in this thrust bearing as a second example of the prior art with respect to debris, moisture and other harmful foreign objects can easily penetrate inside the thrust bearing from the outside, and conversely, grease and other lubricants filled inside the thrust bearing can easily leak to the outside.